The present invention relates to a weft reservoir for fluid-jet looms, and more particularly relates to improvement in construction of a weft reservoir of a type on which a weft is wound for prescribed times on a reservoir drum made up of conical and cylindrical sections by means of a yarn guide rotating in synchronims with loom rotation and subsequently supplied to the main nozzle of the loom after reservation by operation of a control pin.
In the arrangement of the weft reservoir in accordance with the present invention, the side closer to the supply source of weft will hereinafter be referred to as "the upstream side" whereas the side closer to the main nozzle is referred to as "the downstream side".
In general, weft insertion starts at a crank angle between 90 to 110 degrees and terminates at a crank angle between 250 and 270 degrees. During this period, the weft is taken out from the weft reservoir first by free delivery and next, just before termination of the weft insertion, by controlled delivery. It is, however, assumed in the following description that the weft insertion in the present invention starts at about 90 degrees crank angle and terminates at about 270 degrees crank angle.
When registered at an operative position on the reservoir drum, the control pin comes in engagement with the weft and hinders its delivery from the reservoir drum. Whereas, when registered at a stand-by position, the control pin is placed out of engagement with the weft in order to allow its free delivery from the reservoir drum.
In one conventional weft reservoir of the above-described type, a control pin is arranged at the cylindrical section of the reservoir drum. This arrangement is usually called as "an internal type". The control pin is usually placed at a stand-by position taken within the reservoir drum, and is registered at an operative position taken outside the reservoir drum at a prescribed moment by operation of a proper cam drive mechanism. More specifically, the control pin advances from the stand-by position and advances into the operative position outside the reservoir drum by operation of the cam drive mechanism at about 270 degrees crank angle whereat a cycle of weft insertion terminates. On the upstream side of the control pin in this state, the weft is wound for reservation about the cylindrical section of the reservoir drum by operation of the rotary yarn guide. At about 90 degrees crank angle whereat the next cycle of weft insertion initiates, the control pin recedes into the reservoir drum and the weft reserved on the cylindrical section of the reservoir drum are subjected to delivery by traction of the main nozzle.
In addition to the controlled delivery of weft from the reservoir drum, the control pin is adapted for separated reservation of weft for respective weft insertion. One pick of weft usually includes several coils of weft wound on the reservoir drum. For example, four coils of weft wound on the reservoir drum form a pick of weft. At delivery, the coils of weft are sequentially delivered from the downstream side.
When the weft reservoir is equipped with a control pin arranged at the cylindrical section of the reservoir drum, the weft is reserved on the upstream side of the control pin on the cylindical section of a uniform diameter. So, even after the control pin has recedes into the reservoir drum, the coils of weft on the cylindrical section do not move in the axial direction of the reservoir drum and are sequentially subjected to delivery at respective positions at which they were initially wound on the cylindrical section. As a consequence, the control pin is not allowed to advance towards the operative position outside the reservoir drum for reservation of weft for the next cycle weft insertion until the coils of weft on the cylindrical section have all been unwound.
The yarn guide rotates periodically in synchronism with the loom rotation but quite independently of the above-described operation of the control pin, in particular its movement between the operative and stand-by positions. As a consequence, the control pin has to be brought to the operative position outside the reservoir drum after the final coil of weft for a certain cycle of weft insertion has been wound on the cylindrical section of the reservoir drum but before the yarn guide comes to the position of the control pin in order to wind the first coil of weft for the next cycle of weft insertion.
In other words, advance of the control pin to the operative position must be completed within an extremely short period from unwinding of the final coil of weft for a certain cycle of weft insertion to winding of the first coil of weft for the next cylce of weft insertion. It is highly difficult in pactice to properly adjust the timing of the above-described movement of the control pin. Even a misstep in the adjustment would disenable separated reservation of weft for respective weft insertion.
In order to remove the above-described inconveniencies inherent to the weft reservoir having a control pin arranged in the cylindrical section, it has been already proposed to use a pair of control pins on a weft reservoir. In the case of this proposed arrangement, the first control pin moves in the area of the conical section and the second control pin moves in the cylindrical section of the reservoir drum, both for control of weft wound on the reservoir drum. In addition to those movements, the pair of control pins reciprocate in the axial direction of the reservoir drum and pass by, at a certain timing, for transfer of weft.
More specifically, the pair of control pins cooperate in the following manner. Before the first cycle of weft insertion is initiated, the first pin in the conical section advances to the operative position outside the reservoir drum and the yarn guide starts reservation of weft for the second cycle of weft insertion on the conical section on the upstream side of the control pin registered at the operative position. At about 90 degrees crank angle whereat the first cycle of weft insertion is initiated, the second control pin in the cylindrical section receds from the operative position into the reservoir drum and the coils of weft which have been reserved on the upstream side of the second pin are one after another subjected to delivery for the first cycle of weft insertion due to traction by the main nozzle.
At about 270 degrees crank angle, the first pin starts to recede from its operative position into the reservoir drum whereas the second control pin advances to the operative position outside the reservoir drum. During this operation, the first and second pins both move in the axial direction of the reservoir drum. More specifically, the first pin moves towards the downstream side and the second pin moves towards the upstream side so that they pass by each other on their courses of travel. At the moment of this passing-by, the coils of weft reserved on the conical section on the upstream side of the first control pin move downstream following the movement of the first control pin, assigned to the second control pin just moving towards the upstream side, and reserved on the cylindrical section of the reservoir drum on the upstream side of the second control pin now registered at its operative position. The first control pin is required to again advance to its operative position outside the reservoir drum before the yarn guide starts to wind the first coil of weft for the third cycle of weft insertion.
In the case of the above-described type of weft reservoir in which a pair of control pins are combined in operative, there is a broader freedom in choice of the timing at which the first pin again advances towards its operative position, inasmuch as the coils of weft reserved on the conical section on the upstream side of the first control pin move on the reservoir drum towards the downstream side on recession of the first control pin into the reservoir drum. Readvance of the first control pin can take place at any moment before winding of the first coil of weft for the next (third) cycle weft insertion is started by the yarn guide.
Despite the simplified adjustment in timing of pin operation, the weft reservoir of this type is accompanied with another fatal disadvantage in assignment of weft between the control pins. At assignment of weft, the coils of weft wound on the conical section on the upstream side of the first control pin shift onto the cylindrical section which is apparently smaller in diameter than the conical section of the reservoir drum. This change in diameter of the coil of weft naturally develops abrupt slack of weft, which is apt to connect to variation in weft metering operation, unsuccessful weft insertion resulted from tangling of adjacent weft and weft slacking resulted from variation in tension. Such troubles are in particular significant when spun yarns and bemberg yarns of smaller stretch are used for the weft.